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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ART_RUNTIME_READ_BARRIER_H_
     18 #define ART_RUNTIME_READ_BARRIER_H_
     19 
     20 #include "base/mutex.h"
     21 #include "base/macros.h"
     22 #include "jni.h"
     23 #include "mirror/object_reference.h"
     24 #include "offsets.h"
     25 #include "read_barrier_c.h"
     26 
     27 // This is a C++ (not C) header file, separate from read_barrier_c.h
     28 // which needs to be a C header file for asm_support.h.
     29 
     30 namespace art {
     31 namespace mirror {
     32   class Object;
     33   template<typename MirrorType> class HeapReference;
     34 }  // namespace mirror
     35 class ArtMethod;
     36 
     37 class ReadBarrier {
     38  public:
     39   // TODO: disable thse flags for production use.
     40   // Enable the to-space invariant checks.
     41   static constexpr bool kEnableToSpaceInvariantChecks = true;
     42   // Enable the read barrier checks.
     43   static constexpr bool kEnableReadBarrierInvariantChecks = true;
     44 
     45   // It's up to the implementation whether the given field gets
     46   // updated whereas the return value must be an updated reference.
     47   template <typename MirrorType, ReadBarrierOption kReadBarrierOption = kWithReadBarrier,
     48             bool kMaybeDuringStartup = false>
     49   ALWAYS_INLINE static MirrorType* Barrier(
     50       mirror::Object* obj, MemberOffset offset, mirror::HeapReference<MirrorType>* ref_addr)
     51       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     52 
     53   // It's up to the implementation whether the given root gets updated
     54   // whereas the return value must be an updated reference.
     55   template <typename MirrorType, ReadBarrierOption kReadBarrierOption = kWithReadBarrier,
     56             bool kMaybeDuringStartup = false>
     57   ALWAYS_INLINE static MirrorType* BarrierForRoot(MirrorType** root)
     58       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     59 
     60   // It's up to the implementation whether the given root gets updated
     61   // whereas the return value must be an updated reference.
     62   template <typename MirrorType, ReadBarrierOption kReadBarrierOption = kWithReadBarrier,
     63             bool kMaybeDuringStartup = false>
     64   ALWAYS_INLINE static MirrorType* BarrierForRoot(mirror::CompressedReference<MirrorType>* root)
     65       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     66 
     67   static bool IsDuringStartup();
     68 
     69   // Without the holder object.
     70   static void AssertToSpaceInvariant(mirror::Object* ref)
     71       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     72     AssertToSpaceInvariant(nullptr, MemberOffset(0), ref);
     73   }
     74   // With the holder object.
     75   static void AssertToSpaceInvariant(mirror::Object* obj, MemberOffset offset,
     76                                      mirror::Object* ref)
     77       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     78 
     79   static mirror::Object* Mark(mirror::Object* obj) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     80 
     81   static mirror::Object* WhitePtr() {
     82     return reinterpret_cast<mirror::Object*>(white_ptr_);
     83   }
     84   static mirror::Object* GrayPtr() {
     85     return reinterpret_cast<mirror::Object*>(gray_ptr_);
     86   }
     87   static mirror::Object* BlackPtr() {
     88     return reinterpret_cast<mirror::Object*>(black_ptr_);
     89   }
     90 
     91   ALWAYS_INLINE static bool HasGrayReadBarrierPointer(mirror::Object* obj,
     92                                                       uintptr_t* out_rb_ptr_high_bits)
     93       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     94 
     95   // Note: These couldn't be constexpr pointers as reinterpret_cast isn't compatible with them.
     96   static constexpr uintptr_t white_ptr_ = 0x0;    // Not marked.
     97   static constexpr uintptr_t gray_ptr_ = 0x1;     // Marked, but not marked through. On mark stack.
     98   static constexpr uintptr_t black_ptr_ = 0x2;    // Marked through. Used for non-moving objects.
     99   static constexpr uintptr_t rb_ptr_mask_ = 0x3;  // The low 2 bits for white|gray|black.
    100 };
    101 
    102 }  // namespace art
    103 
    104 #endif  // ART_RUNTIME_READ_BARRIER_H_
    105